Hazel crust fungus

Hazel crust fungus, caused by the pathogen Vuilleminia coryli, is a significant fungal disease that primarily affects Corylus species. This fungus functions as a parasite and saprotroph, colonizing the bark and cambium of branches, which eventually leads to localized necrosis and dieback of the woody tissue.

The disease targets hazelnut and filbert trees, frequently manifesting on branches that have been weakened by environmental stress or physical damage. The fungal colonization disrupts the vascular integrity of the branch, severely limiting the tree's ability to transport nutrients, which leads to reduced yields and branch mortality.

Key symptoms include visible fungal fruiting bodies that appear as crust-like or leathery sheets on the surface of the bark. These structures may cause the bark to crack, peel, or exhibit discoloration. Over time, the affected areas become brittle and may serve as entry points for secondary opportunistic pathogens.

The spread of Vuilleminia coryli is largely dependent on high humidity and rainfall, which facilitate the release and dispersal of spores via air currents. The pathogen thrives in poorly ventilated orchard environments where moisture remains on the canopy for extended periods, allowing for rapid colonization of susceptible host tissue.

Effective management requires a proactive approach centered on orchard hygiene. This includes the systematic removal and destruction of infected wood to reduce spore pressure. Ensuring proper spacing and pruning to improve air circulation significantly lowers the risk of infection. Chemical control during the dormant season may also be necessary in high-risk areas.